FIG. 1 is a side cross-sectional view showing one example of winders in the prior art, in which a drive roll 1 is held from a drive roll bracket 2, and it also forms a motor-containing roll which rotates when an electric power is received from a power source 3. The drive roll bracket 2 has its one end fixedly secured to a slider 4. Accordingly, if the slider 4 slides vertically along a guiderail 5, then the drive roll 1 also slides vertically together with the bracket 2. Reference numeral 6 designates a bobbin holder, which is rotatably supported by a bearing 8 fitted in a frame 7, and which also can tightly fit and hold a bobbin around its outer circumference by publicly-known means. Accordingly, if the drive roll 1 is driven as press contacted onto the surface of a bobbin (not shown) held around the outer circumference of the bobbin 6, then the bobbin and the bobbin holder rotate at such rotational speed that they have a circumferential speed equal to the circumferential speed of the drive roll 1, so that when a yarn is supplied while being traversed on the circumference of the bobbin, the yarn is positively wound to form a wound thread package 9. Though various means (not shown) have been known with respect to the structure for applying the press contact force against the wound thread package 9 and the bobbin to the drive roll 1, in any way it is an essential condition for obtaining a wound thread package of good shape to apply a press contact force P that is uniform along the widthwise direction of winding of the wound thread package 9 and that is appropriate. Especially, in case that two or more wound thread packages 9 are formed on a bobbin holder 6 as shown in FIG. 1, or even in case that a single wound thread package 9 is formed if the width of winding becomes large, then the press contact force is apt to become uneven along the direction of width of the winding, so that a wound thread package of good and uniform quality is hardly obtained. In addition, for the purpose of applying a press contact force that is uniform along the direction of width of the winding, it is necessary that the bobbin holder 6 and the drive roll 1 should maintain a very good parallelism over the entire region of the sliding interval of the slider 4, and further, it is necessary that the bobbin holder 6 which has a smaller diameter than the drive roll 1 and which is cantilever supported should have a higher rigidity and should not be flexed by the press contact force P and the weight W of the wound thread package. Accordingly, it has been heretofore necessitated to raise the design rigidity of the bobbin holder 6 as high as possible to maintain high working accuracies, such as straightness, rightness, fitting tolerance, etc. of the respective parts, such as the frame 7, guiderail 5, slider 4, drive roll bracket 2 and drive roll 1, and also to raise the accuracy in assembly. The above-mentioned is an example which has been manufactured and used up to a winding speed of about 2,000 m/Min. though it has been accompanied with difficulties. However, recently, in the spun yarn winding process for synthetic fiber yarns, a spin-draw system or a POY (partially orientated yarn) system has been developed. In these systems, a winder for a high speed large package (a large wound thread package) having a winding speed of 3000-4000 m/Min. is required, and further, if the rotational speed of the bobbin holder is raised up to 12,000-14,000 rpm and if the cantilever projection length is extended up to 350-500 mm, then with the simple bearing support, as shown in FIG. 1, the bobbin holder would resonate within the operating rotational speed range, so that a violent vibration is generated which makes winding impossible. Therefore, a winder, as shown in FIG. 2, has been proposed.
Explaining now the principles of a way of avoiding said resonance with reference to FIG. 2, reference numeral 10 designates a motor-containing drive roll held by a drive roll bracket 11, and said drive roll bracket 11 has its one end fixedly secured to a slider 12. This slider 12 is constructed in such manner that it can slide vertically up and down along a guiderail (not shown) and it can apply a press contact force to a bobbin and a wound thread package (not shown) on a bobbin holder 13 with publicly-known means, and with respect to this point, the construction is similar to that shown in FIG. 1. Reference numeral 14 designates a bobbin holder shaft for the bobbin holder 13, which is rotatably supported by bearings 17 which are resiliently supported from a frame 15 via springs 16. The thus constructed bobbin holder 13 and bobbin holder shaft 14 in FIG. 2 can have their lower order resonant rotational speed set as an specific value within a given range by appropriately selecting their weight distribution and the elasticity of the springs 16, and therefore, if this is set at a value lower than the operating range, then the vibration that is harmful for winding can be prevented. In addition, since the bobbin holder 13 and the bobbin holder shaft 14 are resiliently supported from the frame 15 via springs 16, they can maintain their straightness without being flexed even under a lower order resonant state (lower than the operating range) or even at an operating state exceeding the resonant point. However, in order to obtain a good wound thread package with a winder having such construction, the problem of incorrect parallelism between the drive roll 10 and the bobbin holder 13 must be resolved.
FIG. 2 shows an initial winding state where a wound thread package is not yet formed. Since the bobbin holder 13 and the bobbin holder shaft 14 are inclined in the direction of a press contact force P while almost maintaining their straightness owing to compression of the springs 16 when they are applied with the press contact force P by the drive roll 1, the press contact force distribution on the bobbin is as shown by a number of graduated arrows in FIG. 2, that is, the force is larger on the bearing side and it is smaller towards the opposite side. Then, as the wound thread package 18 grows and its weight W becomes successively larger, as shown in FIG. 3, the bobbin holder 13 and the bobbin holder shaft 14 are integrally inclined substantially, so that almost all the press contact force P is applied to the end of the wound thread ball on the bearing side, and thus there occurs irregular traverse or yarn drop along the end face of the wound thread package on the bearing side, which makes the winding impossible. Strengthening the springs 16 to reduce the inclination of the bobbin holder 13 would result in the rise of a resonant point, and since high speed winding becomes impossible because of violent vibration, this approach cannot be a solution. As described above, in a high speed winder, the way of mounting the drive roll in the prior art had a defect in itself.